1. Field of the Invention
The present invention relates to a camera capable of discriminating between an exposed film frame and an unexposed frame on the basis of information magnetically recorded on an area assigned to each imaging frame. More particularly, the present invention relates to a camera capable of detecting the unexposed frame next to the last exposed frame when a partially used photographic film is wound back into its cartridge, the cartridge containing both exposed and unexposed film is removed from the camera and is subsequently reloaded into the camera, and the film is advanced out of the cartridge, automatically to locate the detected next unexposed frame in the exposure position, so that photography with the same roll of film can be resumed with no waste.
2. Description of the Related Art
Photographic film cartridges are described in U.S. Pat. Nos. 4,834,306 and 5,174,519 (corresponding to Japanese Patent Laid-Open Publn. No. 2-124564 ), in which the film roll of an unused photographic film cartridge of this type is completely accommodated within the cartridge. To begin using the photographic film, the film spool is rotated to advance the leader of the photographic film via the film passage outside the cartridge. It is thus not necessary to manipulate the film leader before the cartridge is loaded into the camera. Another photographic film cartridge of a self-advance type is also known in which the film with a magnetic recording layer is contained in the cartridge. Photographic information and film information are recorded by a magnetic head on the magnetic recording layer of an exposed frame while the film is advanced by one frame. The photographic information includes the exposure value, the print format, the date of exposure, and the like, and the film information includes the ISO speed, emulsion data, and the like.
Another type of camera capable of reloading a partially used photographic film in a cartridge is also shown as described in U.S. Pat. No. 4,864,332. The photographic film cartridge for this camera has a film leader advance function and contains the film whose leader is formed with a magnetic recording area. When the film having unexposed frames is rewound into the cartridge, information as to the position of the unexposed frame next to the last exposed frame is written by a magnetic head on the magnetic recording area to allow the unexposed frames to be used later. When this cartridge is reloaded into the camera, the frame position information is read by the magnetic head, and the next available unexposed frame is automatically located in the exposure position. Because the photographic film cartridge used with this camera can be removed and reloaded before all frames have been exposed, it is possible to use the photographic film without loss of frames.
Generally speaking, information can be magnetically recorded relatively easily, but reading magnetically recorded information is difficult. To reliably read magnetically recorded information, it is necessary to use a device for detecting the speed of film advance with high precision and to provide a reproducing circuit including an amplifier for amplifying weak signals detected by a magnetic head at a high S/N ratio. Such a device and circuit for reliably reading magnetically recorded information complicate the structure of a camera and make it expensive, and are not suitable for amateur cameras. It is difficult to provide a camera suitable for use by amateurs which is capable of reloading a partially used photographic film and resuming photography starting with the unexposed frame next to the last exposed frame.